Radioactive primed resonant window for high-frequency discharge devices



Sept. 22, 1953 T. G. PRESCOTT 2,652,618

7 RADIOACTIVE PRIMED RESONANT WINDOW FOR HIGH-FREQUENCY DISCHARGE DEVICES Filed Dec. 26, 1952 2 Sheets-Sheet l THOMAS G. PRESCOTT INVENTOR.

- wam ATTORNEY Sept. 22, 1953 T G' PRESCOTT 2,652,618

RADIOACTIVE FRI MED RESONANT WINDOW FOR HIGH-FREQUENCY DISCHARGE DEVICES Filed Dec. 26, 1952 2 Sheets-Sheet '2 FIGS 5 FIGS THOMAS e. PRESCOTT INVEN TOR.

ATTORNEY Patented Sept. 22, 1953 RADIOACTIVE PRIMED RESONANT WINDOW FOR HIGH-FREQUENCY DISCHARGE DE- VICES Thomas G. Prescott, Beverly, Mass., assignor to Bomac Laboratories Inc., Beverly, Mass, a corporation of Massachusetts Application December 26, 1952, Serial No. 327,976

2 Claims.

This invention relates to high-frequency gaseous discharge switching devices, and more particularly to said devices employing a dielectric resonant window member primed with a radioactive material.

In radio direction and ranging systems, switch ing devices are employed to permit the use of a single antenna for transmitting and receiving high-frequency signals. During transmission at the high-power level, the sensitive receiver is decoupled by the switching device referred to as a transmit-receive tube. Discharge of a gaseous medium within a resonant cavity effectively blocks the transmitted pulse from the receiver branch of the circuit, and permits essentially all of the signal power to pass to the antenna.

A second switching device commonly found in such systems is the anti-transmit-receive tube. This device decouples the transmitter when a returning signal is received, and prevents the absorption of any energy from the weak signal into the transmitter.

Both of these devices employ a metallic frame member with a central resonant aperture enclosed by a dielectric material. Electromagnetic wave energy of a desired frequency when transmitted to the switching tube will effect a breakdown of the gaseous medium within the evacuated envelope of the device when a predetermined voltage potential exists across the aperture. The transmit-receive tube commonly employs two such apertured frame members, one coupled to the transmitter branch of the circuit, and the other connected to the receiver. The antitransmit-receive tube, however, employs only one such member coupled to the transmitter.

Prior art devices employ a radioactive material in the vicinity of the input resonant window member to furnish a source of electrons in the region of the resonant window, and thereby lower the initial potential necessary to cause ionization of the gaseous medium.

Radioactive cobalt chloride or cobalt nitrate is placed on the low-pressure side of the window member, or on the walls of the tube in the vicinity of the window member. During operation of the radar system, the radioactive material is subjected to bombardment by the ionization of the gaseous medium.

.With the increase in power output in radar systems, the intense ionization at the time of discharge causes rapid decomposition of the radioactive material. As a result, the life of the protective switching device is shortened.

.A further disadvantage is found in the method of applying the radioactive material in prior art devices. The material is generally applied on the surface of the window member, or on the inner walls, and may be accidentally wiped off during subsequent processing operations. This not only affects the performance of the device, but may be injurious to health.

It is an object of the present invention to provide an improved source of radioactivity in a dielectric enclosure member.

It is a further object to provide an improved source of radioactivity which will withstand intense ionization.

It is still a further object to provide an improved method of radioactively priming a dielectric enclosed resonant apertured window member of a high-frequency gaseous discharge device.

In accordance with the teachings of the invention, I provide for the embedding of a source of radioactivity in the dielectric member during the process of sealing the dielectric material and metallic window frame member. Alternatively, I provide a radioactive priming in a dielectric coating surrounding the resonant aperture of a metallic window frame member. The radioactive material is embedded in the coating, and the completed window assembly is hermetically sealed to the waveguide envelope with the primed surface exposed to the interior or lowpressure side of the protective device.

Other objects, features and advantages will be apparent from the following detailed description and appended drawings in which:

Figure 1 is a longitudinal cross-sectional View of a broad-band transmit-receive device;

Figure 2 is a cross-sectional view along the line 11-11 in Figure 1;

Figure 3 is a detailed sectional view along the line III-III in Figure 2;

Figure 4 is a vertical-sectional view of an anti-transmit-receive device embodying the invention;

Figure 5 is a sectional view of an alternative embodiment of my invention;

Figure 6 is a detailed sectional view along the line VI-VI in Figure 5.

Referring to Figure 1, the illustrative embodiment of the present invention shown is a bandpass transmit-receive switching device. A predetermined length of rectangular hollow pipe waveguide I has secured thereto, by conventional vacuum sealing techniques, an input flange 2 and an output flange 3 with holes 4 in said flanges for mounting purposes.

At spaced intervals of approximately one quarter of a wavelength of the desired frequency, iris sections 5, 6, and 'l are secured to the inner walls of waveguide i. A tuning screw 8 is disposed within each iris section to adjust the dimension of the capacitive gap 9 to the desired frequency.

Disposed at the open ends of said waveguide l and hermetically sealed thereto are resonant window assemblies 9 and ill.

Radio frequency power transmitted to the device passes therethrough by-means of apertures H and i2, hermetically sealed by a dielectric member, desirably glass. The. device, is evacuated and filled with a gaseous. atmosphere selected to break down into a gaseous discharge when a predetermined voltage potential is presented across resonant aperture It and gaps 5. When the low-power returning signal is received, it will not be blocked by a gaseous discharge and can pass to the receiver branchofv the. circuit connected to output flange 3,.

Figure 2. illustrates ingrcaterdetail the C011." struction of window assemblies. 5. and Ill. The

metallic window framefil is provided. with a resonant aperture enclosedbya dielectric member. 22, desirably glass, hermetically sealedv thereto. The point of seal, 23. rises. slightly higher than th plane of the other surfacesand is, the region fusing between the metallic oxide and molten glass. A narrow margin. 2.5 alongthe perimeter of the metallic section-,. is provided with a suitable soldering agent for sealing said, section, to the length of waveguide l.

The window. assembly. is first processed according to conventional methods of sealing glass to metal. The. metallic. section 2i. is thoroughh cleaned and then baked in an atmosphere of wet hydrogen to remove. any occluded gases. A layer of oxide is next deposited on said section by heating and then cooling in air,. or. an. oxidieing atmosphere. A glass blank 22. of, predetermined dimensions toenclose the aperture in said metallic section is then-..positioned on said section- According to the teachings of my invention, I provide several drops of.adilutedradioactive material onv said glass blank, 22. Desirably, each drop is applied, and then. smeared across the glass. Lines 25 indicate. the, approximate location of smears after application. The primed glass blank. and metallicsection. are; then. heated to the temperature necessary to. fuse the glass and metal. inavacuumtight sealasat 2.3.

In the selected embodiment, I employ as a priming materialradioactive cobalt chloride or cobalt nitrate. An aqueous solution. is prepared by diluting the radioactive material with water to a concentration. of approximately 25. to 50 hundredths of a microcurie, per; drop; or -.micro.- curies per cubic centimeter.

Since it is at the inputendof the, device that the high-radio frequency power is presented at the resonant Window. I. provide the source of radioactivity at this endto aid. in ionization of the gaseous atmosphereewithin the device. Window assembly 9 sealed in flange 2, therefore, has. the radioactive cobalt chloride or cobalt nitrate embedded in glassblank H.

Another protective device embodying a radioactive primed resonant window member is shown in Figure 4. The window assembly includes a metallic frame 4! with a resonant aperture enclosedby glassblank 42. The assembly is hermetically sealed toone end. of ase t on of 6- tangular waveguide 43, desirably, a quarter of a wavelength long with an end plate 44 hermetically enclosing the other end thereof. Flange 45, with screw holes 46, ma be attached to adapt the tube for mounting in an E or H plane seat of a waveguide system. Diaphragm 47, is supported within thegwaveg-uide 43, to-tune the device to the desired frequency. The internal enclosed chamber 48 may be evacuated and filled with an ionizable gas by means of exhaust tubulation 49.

The window'assembly is radioactively primed according to the--method of this invention, and may be constructed substantially as shown in Figure 2;

In Figures 5. and;6, I have illustrated a resonant window constructed according to an alternative method of my invention, and suitable for use in either the device shown in Figure 1 or Figure 4.

In this method, I treat the metallic window frame 5|, similarly by-pre-oxidation. Next, a suspension. of, powdered glassand a suitable suspending agent suchas. gumtragacanth or water is. prepared. This...suspension is applied to the entire surface of one. side. of, the window frame, as at 52, with the exception of a narrow area 53, along. the. periphery of said. frame.

After. drying;,,.the. coated area. 52is primed with a.radioactive.material,..diluted to the concentration previously specified. Lines 55 indicate the appliedprimingbythe smearing of drops of the luted. radioactive material. Following this priming,.. the glass coated. and primed metallic frame. member may be. heated by conventional tcchniquessuch. as firing. ina non-oxidizing atmosphereuntilthecoating isreduced to a plastic state,.and.forms.a glaze. onthe surface.

Following. a. cooling period, the assembly is completed. b positioning: glass blank 54, and sealing said blank tothe. frame by conventional metal to glassscaling techniqueswith the point of seal as. at. 56..

While I have shown and described several illustrativeembodiments, various. modifications will be apparent. to. personsskilled-inthe art. For instance, in the method; of coating the metallic frame member witha dielectric primed material, the, stepsof firing thecoating and sealing the glassblank to saidmetallic member may be combinedintoone step to. expedite the manufacturing 1 process.

The invention is, therefore, claimed in any modifications or variations falling within the scope of the-appendedcla-ims- What. I; claimand desire to secure by Letters Patent is:

l A- method of radioactively priming a resonant window for high-frequency discharge devices, said; resonant window having a metallic frame member provided with: acentral resonant aperture and' a dielectric enclosure member covering said aperture, comprising the steps of depositing a thin film of: metallic oxides on said apertured metallic frame member, positioning a dielectric; enclosure member thereon, deposi ing a plurality of dropsof an aqueous radioactive solution having. a concentration of approximately 5 microcuries. percubic centimeter on said positioneddiele'otriclenclosure member and heating said positioned members to the temperature nec essary to fuse the-dielectric material and metallic oxides inavacuumtight seal.

2. A method. of. radioactively priming a resonant window. for. high-frequency discharge de vices, said, resonant window having a metallic frame member. providedwitha central resonant aperture, a dielectric coating covering substantially all of one side of said apertured metallic frame member and a dielectric enclosure member covering said aperture, comprising the steps of depositing a thin film of metallic oxides on said apertured metallic frame member, coating substantially all of one side of said apertured frame member with a prepared suspension composed of a powdered dielectric material and a suspension agent, drying said suspension, depositing on said coated surface a plurality of drops of an aqueous radioactive solution having a concentration of approximately 5 microcuries per cubic centimeter, heating said dielectric coated and primed metallic frame member to a 15 2524268 temperature necessary to bond the primed coating and metallic oxides, positioning a dielectric enclosure member on said coated frame member and heating said positioned members to the temperature necessary to fuse the dielectric material and dielectric coating in a vacuum tight seal.

THOMAS G. PRESCOTT.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Fiske Sept. 3, 1946 McCarthy Oct. 3, 1950 Number 

1. A METHOD OF RADIOACTIVELY PRIMING A RESONANT WINDOW FOR HIGH-FREQUENCY DISCHARGE DEVICES, SAID RESONANT WINDOW HAVING A METALLIC FRAME MEMBER PROVIDED WITH A CENTRAL RESONANT APERTURE AND A DIELECTRIC ENCLOSURE MEMBER COVERING SAID APERTURE, COMPRISING THE STEPS OF DEPOSITING A THIN FILM OF METALLIC OXIDES ON SAID APERTURED METALLIC FRAME MEMBER, POSITIONING A DIELECTRIC ENCLOSURE MEMBER THEREON, DEPOSITING A PLURALITY OF DROPS OF AN AQUEOUS RADIOACTIVE SOLUTION HAVING A CONCENTRATION OF APPROXIMATELY 5 MICROCURIES PER CUBIC CENTIMETER ON SAID POSITIONED DIELECTRIC ENCLOSURE MEMBER AND HEATING SAID POSITIONED MEMBERS TO THE TEMPERATURE NECESSSARY TO FUSE THE DIELECTRIC MATERIAL AND METALLIC OXIDES IN A VACUUM TIGHT SEAL. 